1. Technical Field
The present invention relates to an image processing apparatus for processing obtained image data, an image reading apparatus including the image processing apparatus, an image forming apparatus including the image processing apparatus, and a computer-readable recording medium recording a computer program for making a computer process obtained image data.
2. Description of Related Art
Electronization of information has been largely proceeded as well as printers, copying machines and multi-function printers have been widely spread these days. This results in increasing cases where document data is created on the basis of a document of a sheet-shaped recording medium (hereinafter simply referred to as a document) so as to deliver the created document data.
On the other hand, as a method for adding additional data to a printed matter, a method using a two-dimensional code has been widely spread. An example of the two-dimensional code is a QR (Quick Response) code. Cellular phones now widespread among a large number of people are equipped with a function to read a QR code. Also, a function to create a QR code is provided as a function of a cellular phone in some cases and is provided as software for a computer in other cases.
When a QR code is added to a document, additional data of the QR code can be embedded in consideration of the layout of the document without requiring a separate area for adding the code and substantially without making human eyes recognize degradation of the image quality of the document. Other data embedding techniques having such characteristics have been also developed. For example, a micro gradation is disclosed in “Security of Paper Document”, Kensuke Ito and four others, [online] Fuji Xerox Technical Report, [searched on Nov. 29, 2008], <URL on the Internet: http://www.fujizerox.co.jp/company/tr/15/download/pdf/t—4.pdf> (hereinafter designated as Known Document 1). A micro gradation is a technique to embed additional data in a design of the document with the design regarded as a page background. The additional data is binarized to be expressed as a prescribed pattern with gradation.
On the other hand, as a method for restraining unexpected copying of a document, a text hiding technique using visible watermark information in halftone screens is known. In the text hiding technique using visible watermark information in halftone screens, a fact that a printer has higher resolution than a scanner is utilized. More specifically, as illustrated in FIG. 20A, a hidden text “Copy Strictly Prohibited” is printed with resolution readable with a scanner. A pattern (a background of visible watermark information in halftone screens) is printed all over the printed surface of a recording medium of paper or the like with resolution not readable with a scanner so that the hidden text “Copy Strictly Prohibited” cannot be noticed by human eyes. Thus, a document as illustrated in FIG. 20B is obtained. As a result, when the document of FIG. 20A is copied, a scanner cannot read the background of the visible watermark information in halftone screens but reads the hidden text “Copy Strictly Prohibited” alone, and hence, a printer does not print the background of the visible watermark information in halftone screens but prints the hidden text. Accordingly, the document of FIG. 20B is copied, and thus, copying can be restrained.